Ligno-cellulosic biomasses may be converted to biochemical products and fuels by means of different conversion processes.
Before entering a conversion process, the harvested ligno-cellulosic biomass is usually subjected to an initial processing for rendering the raw ligno-cellulosic biomass compatible with the conversion process and equipments.
A problem arising in handling raw ligno-cellulosic biomasses received in the conversion plant is the presence of external contaminants, such as stones, gravel, sands, sand, dust, clay, metal objects which are present together with the ligno-cellulosic biomasses.
It is also desirable to remove inorganic components of the raw ligno-cellulosic biomass, such as silicates, salts and mineral elements, which are detrimental for the conversion process or equipment.
There is also the need to raise the water content of the raw ligno-cellulosic biomass, which in some cases are received in the conversion plant very dry.
Different equipments and processes have been developed so far for preparing the raw ligno-cellulosic biomass to be further processed.
One approach is to carry out the preparation steps sequentially. As an example, the external contaminants may be first removed from the raw ligno-cellulosic biomass, for instance by means of air floatation equipments, and metallic objects are removed by means of magnetic separation devices. Thereafter, the raw ligno-cellulosic biomass may be treated with water and optionally additives, thereby washing the biomass and increasing its water content. Different methods for washing and/or soaking the biomass are used, typically providing mechanical agitation of the ligno-cellulosic biomass. In this case, an extended biomass handling section is present in the conversion plant, said biomass handling section containing many equipments, usually connected with conveyor belts, to convey the biomass. The distributed approach increases the capital and operative costs, as well as the risk of failure.
A different approach is to integrate the preparation steps into a unique equipment. As an example, in U.S. Pat. No. 8,771,472 an apparatus and a related methods for treating material by cutting, soaking and/or washing of the material are disclosed. The apparatus comprises a receptacle, a discharge element with a vortex generator and pumping means arranged to pump fluid and material from the receptacle towards the vortex generator, wherein the vortex generator and pumping means in combination are adapted to generate a vortex in the form of a conic helix in the fluid extending into the receptacle. The pump means includes a pump arranged downstream of the discharge element that also pumps the fluid with cut material through the discharge element toward a separator that separates out a stream of fluid comprising substantially all the cut material from the fluid. The separation may be embodied in the form of a screw press, a filter or centrifuge or means of for sedimentation of the treated material and the residual stream (i.e. the fluid containing substantially no cut material) separated out in the separator is feed back into the receptacle by a recirculation flow line.
However, when the apparatus disclosed in U.S. Pat. No. 8,771,472 is used for treating a ligno-cellulosic biomass stream, such as straw stream, the pumping means are subjected to be easily clogged due to the tough, fibrous nature of the ligno-cellulosic biomass. In addition, in U.S. Pat. No. 8,771,472 the apparatuses and systems used for separating the residual stream from the fluid comprising the cut material involve a significant consumption of mechanical energy (e.g. in the case of a screw press) and/or are subjected to be clogged (e.g. in the case of a filter). Furthermore, in case sedimentation means are used for the separation, as the vortex completely mixes the solid particles in the liquid, the solid/liquid separation through sedimentation normally requires a long time.
In U.S. 2008054108 a pulper having a tank for receiving materials to be shredded and a drive having a rotating hub within the tank id disclosed. A rotor is fixed to the rotating output of the drive, the rotor comprising an annular rotatable hub and a plurality of vanes projecting generally axially from the hub. Each of the vanes has a contour that is swept back from the direction of rotation, at least adjacent the radially outermost portion thereof. The vanes have a side edge facing an axial direction and a plurality of teeth are provided on the side edge of the vanes adjacent the radially outermost portion thereof for providing rapid shredding of material with a reduced energy requirement.
WO 2010/081476 discloses an apparatus having the function of in-feeding and dewatering biomass so as to control water content in biomass before the dewatered biomass is introduced into a process reactor in a plant for the production of, for example, bio-ethanol. The in-feeding and dewatering processes are carried out at a pressure higher than or equal to the pressure inside the process reactor providing the advantage of a fluid tight sealing of the process reactor and facilitating its continuous feeding.
WO 2013/105034 discloses a composition obtained by a process for pretreatment of ligno-cellulosic biomass which allows controlling the xylose ratio of the pretreated biomass.
It is desirable that a low amount of water is used for processing of the raw ligno-cellulosic feedstock before entering the conversion process, as the water in excess has to be treated in a waste water facility. Thereby, a trade-off between amount of water used in the treatment and effectiveness of the treatment is desirable.
It is also desirable that the process uses a low amount of energy, which is both thermal energy from heating the process water and electrical energy for supplying mechanical agitation means.